Name: ______________________________________________ Spring 2019 Quiz 6.101 Introductory Analog Electronics Laboratory NOTE: SHOW ALL CALCULATIONS FOR ALL ANSWERS BUT THE MOST OBVIOUS! [This will allow for partial credit for wrong answers.] Please look through the whole quiz before beginning. There are lots of questions, but most of them are very easy. It’s always good test-taking procedure to look over the whole quiz before deciding where to start, and so you can plan your time. To receive full credit values must also indicate units eg; volts, mv, ma, uF, pF, sec, ms, ohm, mohm, mHz, etc . Where numerical values are required, the answer must a number and not an equation or ratio. If the sign is negative, include the sign for full credit. 1 sheet double sided handwritten notes only. If needed, you may use these values for constants V T (thermal voltage at 25 deg C) = kT/q = 26mv pi = 3.14, sqrt(2) = 1.41 Problem 1 /16 Problem 2 /6 Problem 3 /16 Problem 4 /18 Problem 5 /6 Problem 6 /4 Problem 7 /9 Problem 8 /8 Problem 9 /17 Total
NOTE: SHOW ALL CALCULATIONS FOR ALL ANSWERS BUT THE MOST OBVIOUS! [This will allow for partial credit for wrong answers.]
Please look through the whole quiz before beginning. There are lots of questions, but most of them are very easy. It’s always good test-taking procedure to look over the whole quiz before deciding where to start, and so you can plan your time. To receive full credit values must also indicate units eg; volts, mv, ma, uF, pF, sec, ms, ohm, mohm, mHz, etc . Where numerical values are required, the answer must a number and not an equation or ratio. If the sign is negative, include the sign for full credit. 1 sheet double sided handwritten notes only. If needed, you may use these values for constants
VT (thermal voltage at 25 deg C) = kT/q = 26mv
pi = 3.14, sqrt(2) = 1.41
Problem 1 /16 Problem 2 /6 Problem 3 /16 Problem 4 /18 Problem 5 /6 Problem 6 /4 Problem 7 /9 Problem 8 /8 Problem 9 /17
Problem 1. [Note: Each question below is worth 2 points, 16 total.]
1a. What kind of response do we expect from this type of circuit; i.e. what will change as we vary the frequency of the source from below resonance through resonance to above resonance? 1b. Under what conditions will the impedance of this parallel tuned circuit be at a maximum? 1c. What are some of the things that the term RPara represents? 1d. What is the resonant frequency of this tuned circuit? fo = Hz 1e. Given an ideal current source (no Ro), no Rpara and a totally ideal transformer and capacitor with RL, what is the bandwidth of this parallel tuned circuit? BW= kHz
With the load resistor removed, and now using REAL components, the bandwidth of the circuit is found to be 6.0 kHz. 1f. What is the value of the parallel combination of Ro and RPara? kΩ 1g. What are the upper and lower –3dB frequencies for this circuit? kHz
Problem 2 [Note: Each question below is worth 2 points, 6 total.] You are designing a full wave bridge USB power supply as shown. Knowing that this is a simple unregulated power supply, there is ripple on the output. You want the ripple to be 4.75V to 5.25V with a 500ma load. The diodes have a drop of 0.6V.
What should the RMS voltage of the secondary be to meet spec? ____________V
What is the minimum value of CF to meet spec for ripple? _______________uF
What is the frequency of the ripple? _______________Hz
Problem 3. [Note: Each question below is worth 2 points, 16 total.]
For the circuit, assume that VBE = 0.6 V.
Assume C1, C2, C3 are AC short circuits at all frequencies of interest. The emitter resistor is 240+10 = 250Ω (there is no 250Ω resistor). βo = βF = 150 3a. What is the configuration of the transistor amplifier above? 3b. Draw the load line on the CE characteristics. Label the Q point. 3c. What is VB (base voltage) for this amplifier? 3f. What is the approximate voltage gain for this amplifier if C2 is removed? 3g. What are the values of gm and rπ for this transistor at the given bias current, at 25° C?
3h. What is the input resistance looking into the base of this transistor, with C2 removed? Note: the following questions all have C2 in the circuit. 3j. Now find the DC input resistance including the effects of R1 // R2. 3k. What value of C1 is required for a –3dB point at 10 Hz?
Problem 4. [NOTE: Each question below is worth 2 points except 4g is worth 4 points, 18 total.] As you may recall from lecture, JFETs are depletion devices that requires a negative Vgs(off) = VP to turn off. Their behavior is described by these formulas and the VI curve show below.
4a. What is IDSS for this JFET at VDS = 10 volts? 4c. What is the quiescent value of VGS for this amplifier? 4d. What is the quiescent value of ID for this amplifier? 4e. Draw the load line on Figure 7 on the next page. Label the Q point. 4f. What is the configuration of this amplifier? 4g. What is Vout with VGS = -3V? 4h. [4 points] What value of R2 is needed to move the Q point to VGS = -3V? 4i. What is the input impedance of this amplifier?
Problem 5 [Note: Each question below is worth 2 points, 6 total.] For the ECG lab, a second order Sallen Key LPF was implemented. What is the slope of the filter in __________________dB/octave (include sign if negative)
__________________dB/decade (include sign If negative)
Draw the circuit for a high pass filter Sallen Key filter. Problem 6 [Note: Each question below is worth 2 points, 4 total.] Describe the function of the following circuit ___________________________________
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Assuming the op-amp is an ideal op-amp with R=100 ohms, what is the output impedance of the circuit? _______________Ω
Problem 7 [Note: Each question below is worth 3 points, 9 total.] In lab, a student was asked to wire up a simple timer circuit (circuit A) to control a LED. When SW is closed and then opened, the p channel MOSFET will turn off once the gate voltage raises pass the gate threshold voltage (VGS(th) = -3V).
Circuit A Circuit B ln(.3333) = -1.0986 ln(.2222) = -1.5041 ln(.1111) = -2.1972 [one or more of these constants may be required for your design] When SW (circuit A) is closed and then open, how long does the LED stay on? _______________sec However, the student miswires the circuit and results in circuit B. Does the circuit B behave in the same manner as circuit A? Explain. ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ If the circuit behaves in the same manner, is 22uf (C1-B) the right value for required for identical timing? If not, what is the correct value for C1-B?
Problem 8 [Note: 8 points total.] For the circuit below, the load resistor (not shown) attached to Vout is very large and can be ignored. The capacitors are of equal value. The forward diode drop is 0.6V.
The input voltage is Vin = f(t) = Asin(Bt). Find A and B for Vin. [ 4 points] A = B = Vout [exact value] = ____________________________________________________[4 points]
Problem 9 [17 points total – with partial credit.] My music sound system is automated so when my landline telephone rings, the sound level of the music being played is attenuated by 6dB. After picking up the phone, the sound level continues to be attenuated by 6dB until the call ends. When the phone is placed down, the sound level reverts to its original level in less than 0.2 seconds. The two wires in a landline are referred to as Tip and Ring (TR). During ringing, a 20 Hz 70 Vpp. signal centered at zero volts is sent to TR activating the electro-mechanical bell. When the phone is picked up, a 10 Vdc signal is present on TR. [This is very simplified for the exam.] When there is no activity the voltage on TR is zero. To isolate the telephone circuit from the audio amplifier an opto-isolator is used. When the circuit is activated, ~10 ma is applied to the LED with a 2V drop which in turn attenuates the audio by turning on the BJT in the opto-isolator. The two “grounds” (different symbols) are electrically isolated from each other. You have drawers full of 1N4004, 2N2222 npn, 2n7000 n-channel MOSFET, 1N750 4.7V Zener, resistors and capacitors. The design can be implemented with BJT(s) or MOSFET(s). The 1N750 may not be needed for some designs. To not impact the telephone line, the input impedance of your circuit must be at least 100k. Design the circuit, specify the values of any resistors and capacitor and specify the value of R2. The circuit must be functional but not necessarily optimized for parts count. Partial credit will be given for circuits with
1. correct input impedance 100KΩ min, 2. designs where the semiconductor ratings are not exceeded, 3. correct response time < 0.2 sec 4. labelled values for resistors and capacitors
work copy – use next page for final version R2=_____Ω Notes: 2N7000, 2N2222 are real 1N750 ideal 4.7V Zener ln(4.7) = 1.548
1. correct input impedance 100KΩ min, 2. designs where the semiconductor ratings are not exceeded, 3. correct response time < 0.2 sec 4. labelled values for resistors and capacitors
THIS COPY WILL BE GRADED R2 = ____________Ω Notes: 2N7000, 2N2222 are real 1N750 ideal 4.7V Zener ln(4.7) = 1.548
